The objective of this study is to determine the physiological function of the carbonic anhydrase (CA) isozymes CA III and CA II in the cytosol and CA V in the mitochondria of skeletal muscle. Our aims are to test the hypotheses: (1) that the specialized function of CA III is to facilitate metabolic CO2 transport out of the cell, ~specialized~ because other CA isozymes facilitate CO2 diffusion through solutions, but CA III does it better; (2) that CA II accelerates the dehydration of H2CO3 in fast white muscle, transporting glycolytic H+ out of the cell and initiating the first leg of a cycle that exchanges intracellular lactate for extracellular HCO3-; (3) CA V is present in the mitochondria to produce HCO3- from CO2 for synthesis of oxalacetate (OAA) and citrate. Hypotheses 1 and 2 will be investigated by measuring intracellular pH with 31P MRS in Type I and II muscles at rest and during graded contraction and comparing the rate and total extent of fall in pH before and after the independent inhibition of CA III by cyanate and CA II by sulfonamides. The facilitation of CO2 transport in a 0.015cm layer of buffer by CA III and CA II will be compared to bring out the special transport properties of CA III. Hypothesis 3 will be investigated in suspensions of skeletal muscle mitochondria by measuring: (a) the effect of inhibition of CA V on citrate and 13C16O2 production from 1-13C pyruvate by mass spectrometer ; (b) the effect of Ca++ and dichloracetate on citrate and 13C16O2 production in the presence and absence of CA inhibitors; and (c) the HCO3- permeability of the mitochondrial inner membrane measured by stop-flow rapid mixing pH apparatus and 18O exchange between C18O16O and H16H by mass spectrometry. Successful attainment of these aims will provide for the first time quantitative characterization of the transport processes mediating the disposal of CO2 and lactate from working skeletal muscle and a basis for elucidating their mechanisms.